textproduct: Quad Cities

KEY MESSAGES

- Widespread showers/storms south of Interstate 80 through early Saturday morning to pose a flash flood threat. There will be a low-end severe threat as well, with localized severe wind gusts possible.

- High pressure will bring a period of much needed quiet and dry weather Sunday through Monday, prior to the pattern becoming more active Tuesday through midweek.

SHORT TERM /THROUGH TONIGHT/

Issued at 214 AM CDT Sat Aug 15 2026

Modest LLJ and stationary boundary near our south has allowed for widespread storms to develop south of Interstate 80. These areas have seen rounds of storms, which are producing heavy rainfall and frequent lightning. There remains a Marginal Risk, level 1/5, for severe weather tonight, with main concerns being precipitation loaded downdrafts producing severe gusts. At this time, confidence is low, with the threat being relatively isolated. Our main concern will be heavy rainfall and flash flooding for the remainder of the night. Locations south of Interstate 80 have already seen rounds of heavy rainfall, with this continuing into early Saturday morning. PWATs over 2.00" are being seen area- wide, with our 00z DVN Balloon coming in with 2.09". Thus, areas of repeating showers/storms can easily see upwards to 2.00"+ of rain, with higher amounts likely. HREF guidance comes in quite high on rainfall, bringing in a swath of very heavy rainfall between the Interstate 80 and Highway 34 corridors. Observational trends have indicated the heaviest swath of rain is currently along/south of Highway 34 so far tonight, which is where we might actually see these higher totals. Although, a strengthening LLJ will push farther north through the night, which may nudge this current axis north a bit. The HREF PMM continues to show the potential for at least 3.00-5.00"+ in the hardest hit areas. Locally higher amounts will be possible. As such, the WPC continues to highlight our area in a Moderate Risk, level 3/4, for Excessive Rainfall and Flash Flooding into Saturday morning. The Flood Watch will remain in effect into mid-morning Saturday.

Saturday morning, we will start to see the thunderstorm activity decrease from west-east, with much of the area trending dry by midday. By late afternoon, a remnant boundary from overnight convection will be draped over the area, roughly near the Interstate 80 corridor. The LLJ will start to increase as another wave moves into western Iowa and tracks east through the day. We will start to see isolated to scattered showers/storms develop along this axis, with coverage increasing into the evening/overnight hours. This wave will push through the area overnight Saturday, dragging a cold front through as well. With this pattern in place, we will once again see a round of overnight showers/storms. Overall, shear will be lower, yet sufficient for a few organized thunderstorms, with sufficient instability for some stronger storms with lightning. PWATs will be well above seasonal norms, generally ranging between 2.00-2.25". Thus, heavy rainfall can be expected in any thunderstorms Saturday night into Sunday AM. Although, this system will feature weaker overall forcing and be more progressive, which should help keep areas of heavier rainfall more localized. Heaviest hit areas can see upwards to 1.00-2.00" of rain from this round of storms, with <1.00" elsewhere. A localized flash flood threat will be seen, with WPC highlighting the whole area in a Marginal Risk, level 1/4, for Excessive Rainfall and locations in west-central Illinois in a Slight Risk, or level 2/4 threat.

LONG TERM /SUNDAY THROUGH FRIDAY/

Issued at 214 AM CDT Sat Aug 15 2026

Sunday Through Monday...

This timeframe will be relatively quiet, as we will be fully post frontal and generally in cool/dry advection by midday Sunday. Upper wave and cold front will be east of the area by early Sunday morning, which will effectively help flatten the ridge that was set up over the area the last week, which brought persistent rainfall. Thus, this will shunt the active baroclinic zone south of the area, with surface high pressure passing over through Monday. A period of quiet and dry weather will be seen, with near seasonal temperatures. Monday looks to be a beautiful day with mostly clear skies. Enjoy this reprieve from the active stretch of weather that the region has been experiencing, as the pattern becomes active once again Monday night through midweek.

Tuesday and Beyond...

Monday night into Tuesday, weak ridging will pass east of the area, pushing the surface high pressure out and resulting in increasing llvl southwesterly flow. Temperatures and moisture will both increase on Tuesday, with best moisture moving in later in the day. LLJ will kick in Tuesday evening and through the night, as a quick- moving upper wave approaches the area from the northwest. A seasonally strong cold front will accompany this wave, providing sufficient surface and upper level forcing for thunderstorms. A brief look at model soundings during this timeframe would indicate the potential for an overnight complex of thunderstorms passing through the area, as we have seen over the last week. The main difference with this system is that it will be progressive, pushing out of the area by early-midday Wednesday and leaving us in a post- frontal airmass through the remainder of the week. The best moisture will move into the area ahead of the cold front Tuesday night, with global guidance indicating 1.50-2.00" PWATs moving in. Thus, heavy rainfall will be on the table with these storms. It's too early to dive into the severe threat, but given the pattern and environment in place, a few stronger storms will be possible.

After this wave pushes out of the area on Wednesday, we will see weak zonal-northwesterly flow set up again over the region. Surface high pressure will pass through late in the week, which should bring a period of mostly dry weather. Although, there remains some uncertainty, as some long term models indicate subtle waves passing through bringing low-end PoPs. NBM favors the mostly-dry forecast, leaving PoPs <20% through Friday. The post-frontal airmass will keep temperatures cooler through the second half of the week, with most in the mid 70s.

AVIATION /06Z TAFS THROUGH 06Z SUNDAY/

Issued at 1240 AM CDT Sat Aug 15 2026

Shower and thunderstorm activity remains steady in the south through the overnight hours with a slow northward progression in shower/storm reach towards MLI and possibly CID. A few gusty winds will be possible at southernmost sites, such as BRL. In the north, fog and/or low ceilings should develop with IFR to LIFR conditions, while the stormy south has more intermittent IFR to LIFR potential. Shower activity diminishes early morning with cigs slowly lifting. VFR conditions are possible in the south during the afternoon. Another chance of showers/storms is forecast towards the end of the TAF period.

HYDROLOGY

Issued at 1122 AM CDT Fri Aug 14 2026

Rainfall ranging from 3 to 6 inches, with locally higher amounts occurred last night across parts of the area. The area was generally two counties wide, running from Keokuk County Iowa into southern Henry County Illinois in the north, and Highway 34 in the south.

More heavy rainfall, potentially another 3 to 6 inches with locally higher amounts, is expected tonight into Saturday morning. Some models are indicating the same areas that were hit last night would get hit again. Other models are slightly further south.

Regardless of the location, soils across the area run from moist to saturated. Heavy rainfall tonight has a high probability of resulting in more flash flooding that may be considerable.

The persistent rounds of rain are causing a slow rise on area rivers.

Based on rainfall through tonight, most rivers are projected to only see within bank rises. However, slight changes in the amount each basin receives over the next two days may cause some rivers to go into flood, especially tributary rivers.

A better way to look at this is to look at the probabilities of reaching minor and moderate flood stages using an ensemble spread of precipitation over the next 10 days.

For the following rivers there is a 30-50 percent probability of achieving minor flood stage through August 24th;

English and Iowa Rivers. Cedar River south of I-80

These rivers also have a 20-30 percent probability of achieving moderate flood stage.

For the Skunk River, the probability of achieving minor flood stage is 30 percent, and 20 percent for moderate flood stage.

For the Wapsipinicon River, the probabilities vary considerably. Anamosa has a 37 percent change of reaching minor flood stage while near DeWitt the probability is 83 percent.

DVN WATCHES/WARNINGS/ADVISORIES

IA...Flood Watch until 10 AM CDT this morning for IAZ051>054- 063>068-076>078-087>089-098-099. IL...Flood Watch until 10 AM CDT this morning for ILZ007-009- 015>018-024>026-034-035. MO...Flood Watch until 10 AM CDT this morning for MOZ009-010.